1. Field of the Invention
This invention relates generally to the field of hydraulic pumps. In particular, the invention pertains to a nozzle for boosting pump inlet pressure using excess recirculation oil flow in an automatic transmission.
2. Description of the Prior Art
Positive displacement hydraulic pumps often operate at variable speeds, especially when the pump is in a vehicle power steering system or a vehicle automatic transmission. The pump is driven by the vehicle engine and therefore must operate through the entire engine speed range. The speed at which the pump is driven can exceed 6000 rpm.
A fixed displacement pump produces more flow than needed at high speed, the excess flow being routed to the pump inlet and bypassing a pump filter.
Fixed displacement pumps used in automatic transmissions typically reach a speed at which the supply pressure is insufficient to force fluid into the pumping volume during the intake period. This lack of fluid cavitates the pumping chamber causing reduction in flow volume, durability wear due to cavitation implosions, and the production of cavitation noise, which is objectionable to the vehicle occupants.
A need exists for a jet pump nozzle that is retained in position with a controlled gap that provides fluid velocities required of an effective jet pump nozzle.